The present invention relates to a carbon fiber for a field electron emitter and a method for manufacturing a field electron emitter.
Field emission from carbon nanotubes (CNTs) has been studied and utility thereof as a display material has been attracting attention.
It is necessary to obtain a strong field in order to achieve field emission. Therefore, the tip of an emitter material must be extremely sharp. CNTs have a large aspect ratio and sharp tips, are chemically stable and mechanically strong, and excel in stability at high temperatures. Therefore, CNTs are useful as the emitter material for field emission.
CNTs which have been studied include: (1) a multi-wall CNT (MWCNT) manufactured using an arc discharge in helium gas or the like, (2) a CNT produced by immersing single-wall CNTs (SWCNTs) manufactured using an arc discharge in hydrogen gas or the like in a solvent, and bundling the SWCNTs after drying, (3) a vapor grown carbon fiber, and the like.
These CNTs are formed into a cold cathode having a large area used for light emitting devices by securing a large number of CNTs on a substrate in the same direction using a screen printing process or the like.
However, the MWCNT and bundled SWCNT are unsuitable for mass production on an industrial scale and therefore increase cost.
On the contrary, the vapor grown carbon fiber can be mass-produced at a comparatively low cost.
Generally, the vapor grown carbon fiber has a structure in which hexagonal carbon layers are grown concentrically around the fiber axis, and opposite ends of the hexagonal carbon layers are closed. Therefore, in order to obtain emission of electrons, opposite ends of the hexagonal carbon layers must be opened using a complicated treatment. Since only the opened ends of such a carbon fiber function as emission tips for electrons, it is difficult to obtain a large number of electron emission tips. In order to obtain a large number of emission tips, it is necessary to perform a very difficult process such as an increase in the fiber diameter or formation of openings in an area other than opposite ends of the carbon fiber.